Using checkboxes

Hey all, I have a form, generated in php, with a lot of checkboxes on it. They are initialized from the db. All checkboxes are in a 2d array and they come through to my processing script fine. The only problem is that the ones that are unchecked do not come through. I know that the post command only sends the checked boxes. What I would like to know is which ones were changed, ie checked or unchecked by the user. Right now I do it by putting a string with the old values in a hidden textbox and comparing those to what I get back in the array. I have been thinking about writing some client side script to produce the differences. Does anyone know if there is a better way to do this? Thanks, Dirk.